During typical use, varying photographic demands require that cameras be fitted with lenses of different focusing capabilities. Inconvenience for the user arises when these fixed-focus lenses have to be changed in order to meet differing demands.
The recently developed "zoom lens" was created to overcome the aforementioned drawbacks by providing a variable focus lens, with a 2.times. to 3.times. zoom ratio, which the user can employ to meet the demands of differing situations.
Most zoom lens designs incorporate telephoto lens sets comprising two lens assemblies--one group of positive power lenses and another of negative power lenses--which move the principal plane forward and shorten the back focal length.
Moving the two assemblies relative to each other alters the air space between them, thereby changing focus.
Recent technical advances in precision camera manufacture has led the industry to miniaturize camera components. Due to their weight and large size, the miniaturization of zoom lenses has become an important item of technical research.
Lens miniaturization can be approached from two directions. The first is to reduce the length of the lens without sacrificing image quality. The other approach is to reduce the number of component lenses; i.e., maintaining image quality and providing a greater zoom ratio, while keeping the length (the distance from the first surface vertex to the film) of the entire lens set the same, but using fewer component lenses. The industry has been making continuous efforts toward achieving both these goals.
One means of shortening the length of the entire lens set is to reduce the radius of curvature of the component lenses. However, reducing the radius of curvature increases the power, which may lead to major aberration changes when Zooming the Lens, making appropriate image quality impossible to achieve.
Increasing the number of lenses can mitigate the need for a small radius of curvature, as so doing allows a reduction in the power of each component lens, which then reduces the aberration produced during Zooming. This method, however, is unsuited to production since the increased number of lenses greatly raises the cost of the device.
U.S. Pat. No. 4,830,476, disclosed an improved zoom lens. The zoom ratio of this patent is, however, only 2.times..
The industry is thus in need of an improved zoom lens which can be miniaturized, provides high image quality, and has a high zoom ratio.
It is thus an object of this invention to provide a miniaturized zoom lens.
Another object of this invention is to provide a zoom lens with improved image quality.
Another object of this invention is to provide a zoom lens with a higher zoom ratio.
A further object of this invention is to provide a new design for a zoom lens assembly.